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[Jonathan Johnson]

There's a lot of discussion here about direct contact with high voltage, but proximity can be just as injurious or deadly, especially when personnel does not have proper safety gear and there is an arc flash nearby. For example, disconnecting a high-current service (even low voltage) while under load -- or connecting high-current service to a dead short -- can result in large quantities of molten metal flying at supersonic speeds. If the arc flash is in the presence of flammable or explosive vapors, the danger is double.

[Mike Sokol]

There's a lot of discussion here about direct contact with high voltage, but proximity can be just as injurious or deadly, especially when personnel does not have proper safety gear and there is an arc flash nearby. For example, disconnecting a high-current service (even low voltage) while under load -- or connecting high-current service to a dead short -- can result in large quantities of molten metal flying at supersonic speeds. If the arc flash is in the presence of flammable or explosive vapors, the danger is double.

Yup.... and here's the thread on the subject for those who are new to the party. http://forums.prosoundweb.com/index.php/topic,147539.0.html

I've got a lot of new information on arc flash safety which I'll post later this week if there's time. Just note that an arc-flash explosion produces a fireball which can be hotter than the surface of the sun traveling faster than the speed of sound. You DON'T want to be in the blast radius.

[Jeff Bankston]

Any time you get into a situation where 600 Volts is considered low voltage its time to walk very very carefully!  I am more than happy to let others have the thrill.

I used to have to work on an inductive welder that used a vacuum tube oscillator running at 13.8 kV.  Fortunately it was fairly well behaved and low maintenance.  We ran it at about 20 Kw, though it was capable of 100 Kw.  Doubt I'll run into any audio stuff putting out that kind of power any time soon though-which is fine by me.

Its amazing to me that he survived-and still has some vision to live by.

the code considsers all voltages 600 and under to be "low voltage". any voltage above 600 is "high voltage" and they also teach that in school. 277/480 is in almost every business that has ballasted lighting. i'v wired up many 480 3 phase rtu's. a guy i worked with got shocked by 2 phases of 480. he was sore for a few days. flash from a ground out is a real danger. the bright light can blind you and the hot bits of molten metal can penetrate the skin and eyes.

[Mike Sokol]

the code considsers all voltages 600 and under to be "low voltage". any voltage above 600 is "high voltage" and they also teach that in school. 277/480 is in almost every business that has ballasted lighting. i'v wired up many 480 3 phase rtu's. a guy i worked with got shocked by 2 phases of 480. he was sore for a few days. flash from a ground out is a real danger. the bright light can blind you and the hot bits of molten metal can penetrate the skin and eyes.

Even though I'm very careful about getting shocked from "low voltage" system, I'm extremely cautious about high-amperage circuits. Because  home and industrial wiring typically have insufficient voltage to cause actual nerve and physical tissue damage with brief exposure, most of the time it's heart fibrillation and stoppage that kills you. However, quick response with CPR and an AED can save your life with little long-term damage. But arc-blast damage is forever as you've seen from some of the pictures. Also know that while not often talked about on electrical sites, many arc-flash victims also suffer profound hearing loss from the blast. And as I've often noted, there's few things worse than a deaf sound engineer. hearing protection is an important part of PPE (Personal Protective Equipment) that's just recently being required for working around high-energy circuits.   

[Stephen Swaffer]

Not to be argumentative, but the only reference to "low-voltage" in the NEC is in the RV section and it defines it there as less than 24 volts (but that def only applies to that section), other places refer to less than 50 volts, otherwise code refers to "under 600 volts" or "over 600 volts".  I don't have access to the NESC and that may define under 600 as low volts, or perhaps NFPA 70e might.  My reference was to the fact that in most facilities have 480 V or lower services, anything under 50 V will be considered low voltage, anything over will be considered and marked high voltage.  It can be confusing-and it can be dangerous if you are not aware and/or thinking.   In my world as an electrician, common vernacular is "low voltage wiring"=less than 50 volts.  If we deal with "over 600 V" well usually spec the voltage.  I am sure larger industrials/POCOs use different terms.

I watched a documentary on an arc flash incident the other night, I don't have the link, but it came up on youtube when I watched one of the previous videos in this post.  The man went into an MCC room that contained both 480 V and 2300 V MCCs.  In haste, he opened a can and did a voltage test-unfortunately he was in a 2300 V can with a 1000 V meter (looked like a Fluke).  The blast literally burned him out of his clothes, he managed to stagger several hundred feet, coworkers saw something glowing in the now darkened building and realized it was a man.  He was coherent and talked with EMTs and told coworkers what his mistake was-but he died the next day.  The video was made by coworkers-and the incident obviously impacted them tremendously as well.

Since many on here work in various facilities that may or may not have "greater than 600V", just make sure you know what that "High Voltage" sign really means. 

[Mike Sokol]

The man went into an MCC room that contained both 480 V and 2300 V MCCs.  In haste, he opened a can and did a voltage test-unfortunately he was in a 2300 V can with a 1000 V meter (looked like a Fluke).  The blast literally burned him out of his clothes, he managed to stagger several hundred feet, coworkers saw something glowing in the now darkened building and realized it was a man.  He was coherent and talked with EMTs and told coworkers what his mistake was-but he died the next day.  The video was made by coworkers-and the incident obviously impacted them tremendously as well.

This is also the best reason to use a high-quality meter for all measurements. I do know that high-end companies such as Fluke and Amprobe take meter arc-flash explosions very seriously, and I would NEVER poke a free Harbor-Freight meter into a service panel. A lot of this comes down to the safety class of the meter, so knowing if you have a Class I, II, III, or IV meter is important. I'm looking for a definitive chart to post here that shows these classes along with max voltages they can be used on. Most of my Fluke gear is Class IV and rated for 1,000 volts AC. But even if an inexpensive Class II meter has sufficient voltage ratings for what you're measuring, if there's a transient/voltage spike on the power line while you're "in the box", it can cause your cheap meter to explode. I think we should start a thread just on voltmeter classes and safety ratings. I'm not up to speed on all of this, so it would be a great education to do a little research and discussion. Is anybody here an meter classification expert who would like to weigh in on the subject?   

[ProSoundWeb Community]